Bay Bridge Shows its 'War on Corrosion'

How do you fight corrosion in 17,399 packed steel wires holding up the world’s largest self-anchored suspension bridge?

Very, very carefully—harnessing the nation’s top engineering minds and technologies. The strategies range from high-tech dehumidification, to new coatings and wraps, to new imaging and magnification tools that can pinpoint flaws in an individual wire.

Such are the details revealed in a fascinating new video, War on Corrosion, produced by the California Department of Transportation (Caltrans).

Caltrans

Caltrans spokesman Bart Ney details the many challenges of fighting corrosion in the Bay Bridge's main cable. "The real work horse of this bridge," the cable contains 17,399 individual wires.

Just under 12 minutes long, the new video is the final installment in the Bay Bridge 360 trilogy hosted by Caltrans spokesman Bart Ney. Bay Bridge 360 is Caltrans’ extensive video documentation of each step of the bridge’s construction.

Bay Bridge 360

Replacing the structure damaged by the 1989 Loma Prieta Earthquake, the new bridge is being designed and built to withstand the largest possible earthquake within 1,500 years, Caltrans says.

Caltrans

The installation of two layers of a Noxyde-based coating are just one step in a complex system to protect the main cable of new bridge from corrosion.

The formal three-part Bay Bridge 360 series details the constructability challenges of the massive project of building the new East Span of the Bay Bridge. The first installment delved into the project’s concrete placement challenges; the second addressed steel post-tensioning.

Now, War on Corrosion offers a detailed look—from the surface of a single wire to the top of the 525-foot tower—at the many corrosion technologies being used to protect the new bridge, which is scheduled to open next year.

“On the new Bay Bridge, the main cable is being armed from the beginning to fight a war that will last its lifetime,” says the narrator.

Corrosion-Fighting Tour

Caltrans cameras follow Ney from the supports underneath the deck to the top of the tower as he discusses the corrosion program that has been developed to protect the new self-anchored suspension bridge from the salty damp air of the Northern California environment.

“Corrosion is the challenge that we face, from the time we buy the steel all the way through the life span of the bridge,” says Ney.

Sanbeji/no-onions/extra-pickles.com

The new Bay Bridge, scheduled to open next year, will replace the structure that collapsed in the 1989 Loma Prieta Earthquake.

The principal challenge is in protecting the nearly-1-mile-long main cable— “the real workhorse of this bridge”—which is comprised of 17,399 individual 5 mm wires.

The treatment begins with galvanizing each wire, coating most of the cable with a zinc-based paste, wrapping and coating that, and more.

Perhaps the biggest challenge was at the top of the bridge tower, where the cable crosses the support twice and wrapping and coating were not options.

Early Skirmish

The video also discusses the project’s “early skirmish” with corrosion in the structure’s 1.2-mile skyway, in which rainwater was collecting in ducts that had to be left open during construction.

Cutting-edge borescope imaging, vapor phase inhibitors, strategic “surgery” and more were just some of the technologies that rode to the rescue.